1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming apparatus. More particularly, the present invention relates to a sheet processing apparatus enabling the miniaturization and cost reduction, and improving the sheet alignment performance.
2. Description of the Related Art
Conventionally, commonly known image forming apparatuses such as copying machines, printers, facsimiles, and multifunction peripherals include an image forming apparatus main body and a sheet processing apparatus for processing sheets. The image forming apparatus main body includes an image forming portion. An image is formed on a sheet in the image forming portion and then the sheet is conveyed to the sheet processing apparatus.
Some of such sheet processing apparatuses include a sheet stacking tray, an intermediate stacking portion disposed above the sheet stacking tray, and a pair of joggers for supporting and aligning the ends in width direction perpendicular to the sheet conveyance direction (hereinafter referred to as lateral ends) of a sheet stack on the intermediate stacking portion. A stapler for performing stapling process to the sheet stack is provided in the vicinity of the intermediate stacking portion.
The above-mentioned sheet processing apparatus can be set either in the stapling process mode in which the stapler performs stapling process to the sheet stack on the intermediate stacking portion, or in the stack mode in which sheets are discharged onto the sheet stacking tray one by one without stapling process. To pursue the miniaturization, cost reduction, usability, and aligning performance, the joggers for aligning the lateral ends of the sheet by movement of the pair of joggers in width direction are not disposed in the sheet processing apparatus main body but disposed downstream in the sheet conveyance direction of sheet discharge rollers (refer to U.S. Pat. No. 6,942,206).
When the sheet processing apparatus is set in the stapling process mode, sheets are sequentially conveyed to the intermediate stacking portion and the pair of joggers, the lateral ends of the sheet stack are supported by the joggers, and after the sheet stack is subjected to stapling process by the stapler, the sheet stack is dropped onto the sheet stacking tray from the intermediate stacking portion by retraction of the pair of joggers in width direction.
The sheet processing apparatus performs stapling process for target sheets separated from the sheet stack on the sheet stacking tray in this way, instead of performing it on the sheet surface of the sheet for a preceding job stacked on the sheet stacking tray. Thus, the sheet stack on the sheet stacking tray can be taken out during stapling process, improving the accessibility to the sheet.
Further, the sheet processing apparatus is provided with a space between the sheet stacking tray and the joggers so that the space makes a sheet stack easy to take out from the sheet stacking tray. When the sheet processing apparatus is set in the stack mode, a discharged sheet from the sheet discharge rollers is passed between the pair of joggers retracted to outward positions in a sheet discharge area and dropped onto the sheet stacking tray directly.
However, the above-mentioned conventional configuration has a problem that, when the sheet processing apparatus is set in the stack mode in which sheets are stacked on the sheet stacking tray one by one without stapling process, the sheets are likely to become disordered resulting in degraded sheet alignment performance.
Since a single sheet is light, the sheet fluctuates due to air resistance while it is falling over a long distance from a sheet discharge port to the sheet stacking tray. Therefore, there has been a demand for a sheet processing apparatus that can improve the sheet alignment performance for a single sheet, with a simple configuration and low cost.